1. Field of the Invention
The present invention generally relates to integrated circuit manufacture, and more particularly to thin films and their production.
2. Background Description
In logic technologies at a size of 90 nm and smaller, the quality and characteristics of polysilicon is a major factor in determining the gate dielectric scalability. In order to reduce depletion capacitance of gate polysilicon, higher doping concentration at the polysilicon and gate oxide interface has been strongly required. This requirement has been met by increasing poly dopant dose and higher temperature activation. However, this approach may create serious gate dopant penetration into the channel which results in threshold voltage shift, surface punch-through, and device instability.
In recent literature, L. Jalabert et al., “Reduction of boron penetration through thin silicon oxide with a nitrogen doped silicon layer,” Microelectronics Reliability, 41, 981–985 (2001), have shown that reduction of boron diffusion is obtained by having nitrogen doped silicon layer at the gate dieletric and gate conductor interface. Jalabert et al. obtained the nitrogen doped interface by reacting disilane and ammonia (NH3) in a low pressure chemical vapor deposition (LPCVD) furnace. Furthermore, it has been shown in the literature that an amorphous silicon layer reduces boron diffusion. There is also evidence that having low carbon concentration (less than 1020/cm−3) in the silicon-germanium (SiGe) region of SiGe hetero bipolar transistors (HBT) can significantly suppress boron out-diffusion caused by later thermal processing steps. Thus, it has been desired to control the introduction of carbon into films.
In most cases, carbon is introduced in the film by adding an organic material in the gas mixture during the deposition of silicon or silicon-germanium films. Carbon also can be implanted in the film, although implantation damage may be caused.
Conventionally, various films have been produced.
For example, U.S. Pat. No. 6,268,299 (Jul. 31, 2001) discloses formation of silicon-rich silicon nitride films used for barrier application. The silicon nitride films are deposited using various silicon containing precursors, e.g., bis-tertiary butyl amino silane (BTBAS), HCD, SiH4, etc., and NH3. The silicon to nitrogen ratio is modulated by changing the flow ratio of the silicon-containing precursor and NH3. The deposition takes place in LPCVD batch furnaces.
U.S. Pat. No. 6,486,015 (Nov. 26, 2002) discloses carbon-rich oxynitride, with reactive ion etching (RIE) selectivity due to carbon in the oxynitride film.
U.S. Pat. No. 6,500,772 (Dec. 31, 2002) discloses plasma enhanced growth of oxynitride and nitride using BTBAS and N2O and NH3. Carbon is incorporated in the nitride and oxynitride films.
U.S. Pat. App. 2003/0020108 (Jan. 30, 2003) discloses decreasing the etch rate of silicon oxide films by doping the film with carbon (p 0038). Silicon oxide films are formed with varying amounts of oxygen, carbon and nitrogen.
U.S. Pat. No. 6,518,626 (Feb. 11, 2003) discloses oxynitride films, with carbon incorporation and etch rate as a function of N2O/O2 ratio, in a batch furnace. Film deposition is by BTBAS and N2O (with or without O2).
The conventional films and methods for producing films have not necessarily provided all of the film characteristics that may be desirable for responding to the challenges of 90-nm and sub-90 nm technology. Nor are there adequately simple, feasible production methodologies for making films to have desired characteristics.